Safe treatment, preservation and management of wastes, particularly, of hazardous wastes, such as radioactive wastes, are very important processes. As an example of the processes of treating, preserving and managing the wastes, waste vitrification that is a process of treating the wastes using glass has been proposed and used, in which radioactive wastes, sludge, contaminated soil, industrial wastes etc. are captured in a glass structure and are prevented from leaking to the surrounding environment, thereby permanently keeping the wastes in isolation.
To perform waste vitrification using a waste vitrification apparatus, a glass forming agent and wastes are melted in a melting furnace. Here, volatile components of the wastes can be exhausted through an exhaust treatment process and hazardous materials, such as radioactive atomic species and heavy metals, stay in the furnace for a predetermined lengthy period of time while being heated to form a part of a glass reticular structure, thereby forming a homogeneous molten glass mixture. Thereafter, the molten glass mixture is discharged from the furnace so that the poisonous materials are formed as a vitreous solid.
A variety of melting furnaces that are classified according to heating types have been proposed. Of the melting furnaces, a cold crucible induction melter (CCIM) is an induction melting furnace which includes a cylindrical melting chamber that has an insulating material placed between a plurality of metal sectors through which a coolant circulates. Further, a high frequency induction coil is provided at a location outside the melting chamber and supplies electricity so that materials contained in the melting chamber can be melted.
The above-mentioned cold crucible induction melter is provided with a molten material discharging part that functions to discharge materials after melting the materials. For example, U.S. Pat. No. 6,620,372 (Date of Patent: Sep. 16, 2003.) and Korean Patent No. 611358 (Date of Patent: Aug. 3, 2006.) disclose molten material discharging devices in which a discharging port is formed through the bottom of a melting chamber and a sliding gate is provided in the discharging port so that a molten material can be discharged through the discharging port by an on/off motion of the sliding gate.
As another example, a cylindrical discharging port that extends to a predetermined length is formed in the bottom of a melting furnace, and a heating unit, such as an induction coil, is provided in the cylindrical discharging port so that a molten material can be discharged from the melting furnace. However, this technique is problematic in that it requires a substantial lengthy period of time for cooling the cylindrical discharging port so that it is impossible to control the flow of the material to be discharged. Another problem of the technique resides in that, when glass is adhered to the cylindrical discharging port, it may not be easy to discharge the adhered glass from the furnace.